If you haven't done your taxes yet, this ad from H&R Block might make you feel even more anxious.

"The Affordable Care Act means big changes this year when you file your taxes," says the young woman in the ad, with a smug smile. She then claims to have read "all 900 pages" of the law so she can offer you a "solution."

We wanted more details about whether the federal law was really making this year's taxes more difficult, so we asked Meg Sutton, the tax firm's senior adviser for tax and health care services.

"The big changes are, really, just filing that return," she said. "And so, getting into the office, recording your income and your household size, that's the biggest change you'll see."

Except people have to do that every year. So we asked if there are new forms people have to file this year because of the health care law.

"No," said Sutton.

When we pressed her, she said the big change is in preparing for the new federal subsidies that millions of Americans will be able to apply for to help them buy individual health insurance policies next year. Because people can start signing up for plans from the new health insurance marketplaces as early as October of this year, a 2012 return could come in handy.

"The 2012 tax return will be used to establish a baseline to determine your eligibility for a tax credit to pay for health care benefits," Sutton said.

Eligibility for the new health insurance subsidies will be based on income and family size. Information from 2012 tax returns — the returns people are filing this year — should be automatically pulled up on a computer screen when people apply for the subsidies this fall.

"But it's just a baseline," says Tara Straw, of the advocacy group Health Care for America Now, which supports the Affordable Care Act.

"Nothing in that return locks people into a certain income or a certain family composition that is unchangeable if it's not representative of their actual situation in 2014," Straw says.

What will actually determine whether people get a subsidy, and how big it will be, isn't what they report on their tax forms this year at all, but how much they estimate they'll make in 2014. That could be the same as what's on their tax form this year, or it could be very different.

So when Straw sees the H&R Block ad saying the Affordable Care Act means big changes this year when you file your taxes, she says it's "fairly misleading."

"Unfortunately right now, with this ad, it sounds like they're just trying to drum up business by emphasizing complications," she says.

"That's actually where companies like H&R Block could be doing a real service if they're actually using their outreach to the community to help educate people on the benefits," says Straw.

H&R Block says it's doing that by offering all its customers a free health care and tax review this year that they say takes about five minutes. They also have a guide to how the law might affect different tax profiles. But as far as filing any new tax forms related to the health care law, those will come in April of 2015.

Shots is the online channel for health stories from the NPR Science Desk. We report on news that can make a difference for your health and show how policy shapes our health choices. Look to Shots for the latest on research and medical treatments, as well as the business side of health. Your hosts are Scott Hensley and Nancy Shute. You can reach the Shots team via our contact form.